Comparative Antibiotic Activities of Ethanol Extracts of Leaves and Inflorescences of Mitracarpus villosus from two different Geographical Regions in Nigeria in Synergy and Antagonism with Conventional Antibiotics

Abstract

Ethanol extracts of leaves and inflorescences of Mitracapus villosus from Ikom and Nsukka in the South-South and South-East geographical regions of Nigeria respectively, were analyzed for bioactivity using agar well diffusion method against four test organisms: Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aereus. Results obtained revealed that the geographical location of the plant as well as its soil composition affects the quantity and quality of secondary metabolites produced by the plant. Results of quantitative phytochemical and soil analysis showed an inverse relationship between certain soil parameters and constituent phytochemicals. Ikom sample has higher nitrogen: 0.160±0.001MEQ/100g compared with Nsukka sample with nitrogen content of 0.065±0.007MEQ/100g. The constituent cyanide in Ikom sample: 0.078±0.000mg/100g is lower than that of Nsukka sample which is 0.127±0.000mg/100g. Also alkaloid of Ikom sample: 1.620±0.004mg/100g is lower than Nsukka sample: 2.107±0.003mg/100g. Soluble carbohydrate in Ikom sample, 0.955±0.000mg/100g is lower than Nsukka sample containing 1.915±0.000mg/100g.  Inhibition zone diameters (IZDs) of Ikom extracts and Nsukka extract showed that Nsukka extract with IZD 27.5±0.07mm has higher bioactivity than Ikom extract with IZD= 14.5±0.07mm against K. pneumonia at concentration of 100.000mg/ml. At concentration of 12.500mg/ml, Ikom extract had no inhibition on all test organisms, but Nsukka extract had IZDs of 12.000±0.000mm and 7.000±0.000mm against E. coli and S. aereus respectively. The MICs for Nsukka extract against E. coli = 12.500mg/ml and S. aereus = 12.500mg/ml are lower than that of Ikom extract: E. coli = 50.000mg/ml and S. aereus = 25.000mg/ml. These imply that Nsukka extract is more potent than Ikom extract against E. coli and S. aereus. In this in vitro study, synergism and antagonism have been consistent with the plant extracts against different test organisms. Nitrofurantoin10µg, had synergy with both extracts against E. coli. Ceftriaxone30µg had synergy with both extracts against S. aereus while Ciprofloxacin10µg had synergy with both extracts against K. pneumoniae and P. aeruginosa. However, antibiotic antagonism was observed with different conventional antibiotics: Ceftriaxone30µg showed antagonism with both extracts against E. coli, K. pneumonia and P. aeruginosa. Gentamycin10µg also showed antagonism with extracts against S. aereus and P. aeruginosa.

Keywords: Bioactivity, metabolites, phytochemicals, synergy, antagonism, inhibition.